Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $227.62   6.626%   $242.7021   $242.70   $242.70   $242.70  
  Purchase #2 $87.96   10.745%   $97.4113   $97.41   $97.40   $97.40  
  Purchase #3 $169.56   7.272%   $181.8904   $181.89   $181.90   $181.90  
  Purchase #4 $10.88   7.509%   $11.697   $11.70   $11.70   $11.70  
  Purchase #5 $239.48   4.167%   $249.4591   $249.46   $249.45   $249.50  
  Purchase #6 $141.62   6.486%   $150.8055   $150.81   $150.80   $150.80  
  Purchase #7 $86.29   7.823%   $93.0405   $93.04   $93.05   $93.00  
  7 purchase totals = $963.41       $1,027.0059   $1,027.01   $1,027.00   $1,027.00